The present invention pertains in general to the removal of fluid from a wellbore in the earth by the use of a plunger lift system and in particular to the determination of the location of the plunger in the wellbore together with well performance parameters.
Plunger lift, the only artificial lift process that requires no assistance from outside energy sources, is ideally suited to a variety of downhole well conditions and applications. Two suppliers of equipment plungers are Weatherford Artificial Lift Systems and Ferguson Beauregard. Plunger lift systems consist of a plunger, often referred to as a piston, two bumper springs, a lubricator to sense and stop the plunger as it arrives at the surface, and a surface controller of which several types are available. Various ancillary and accessory components are used to complement and support various application needs.
In a typical plunger lift operation, the plunger cycles between the lower bumper spring located in the bottom section of the production tubing string and the upper bumper spring located in the surface lubricator on top of the wellhead. As the plunger travels to the surface, it creates a solid interface between the lifted gas below and produced fluid above to maximize lifting energy.
The plunger travels from the bottom of the well to the surface lubricator on the wellhead when the force of the lifting gas energy below the plunger is greater than the liquid load and gas pressure above the plunger. Any gas that bypasses the plunger during the lifting cycle flows up the production tubing and sweeps the area to minimize liquid fallback. The incrementation of the travel cycle is controlled by a surface controller and may be repeated as often as needed.
Plungers, a major component in a plunger lift system, are installed in the tubing string and provide a solid interface between the produced fluid column and lift gas. Weatherford and Ferguson Beauregard have various plunger designs available. Among these are lightweight brush types for low-pressure applications; solid plungers made of 4140 steel are available in different lengths, dependent on bottomhole pressure; plungers with spring-loaded pads that offer enhanced sealing against the tubing during upward travel; and for wells with high paraffin content, plungers with a spiral design. In addition, Weatherford supplies special application plungers for use in coil tubing and highly deviated wells.
Bumpers function as springs in plunger lift systems to absorb the impact of the plunger when it reaches the bottom of the well, and to prevent potential damage to downhole fishing-neck profiles. These subsurface bumpers seat in either a seating nipple, tubing stop or collar stop. Models available include low-cost, freestanding subsurface bumpers for use when a seating device exists in the well, and modular subsurface bumpers that accept several different bottom attachments, such as a hold-down device, cup seal, or standing valve.
Weatherford lubricators are used in plunger lift systems to sense and stop the plunger as it arrives at the surface. They have spring-loaded cushions to absorb the shock and prevent damage to the plunger. Two designs offered by Weatherford are a standard plunger lubricator that incorporates both the flowcross which attached the flowline to the tubing and the needle valve outlet, and a lubricator with the added features of a plunger trap and optional sensor. Both models are available in single or dual outlet configurations.
Various controllers control pneumatic-actuated valves for time-cycled intermittent gas lift, plunger lift, or a combination of both. Several models are offered with features to match the type of control needed for specific applications. Among these are low-cost timers with optional solar panels and rechargeable batteries, high-end controllers that feature input for variable flow time, and self-adjusting automatic time-cycle controllers.
A variety of plunger lift accessories and production enhancement components are available. Magnetic shutoff switches, flow tees, various types of packing elements, collar and tubing stops, standing valves, and seating nipples offer support enhancement to the entire system. Chokes, motor valves, drip pots and regulators, and solar panels complement and assist in maximizing production performance.
A plunger-lift system is a low-cost, efficient method of increasing and optimizing production in oil and gas wells, which have marginal flow characteristics.
Functionally, the plunger provides a mechanical interface between the produced liquids and gas. Using the well""s own energy for lift, liquids are pushed to the surface by the movement of a free-travelling piston (plunger) traveling from the bottom of the well to the surface. This mechanical interface eliminates liquid fallback, thus boosting the well""s lifting efficiency. In turn, the reaction of average flowing bottom hole pressure increases inflow.
Plunger travel is normally provided by formation gas stored in the casing annulus during a shut-in period. As the well is opened and the tubing pressure allowed to decrease, the stored casing gas moves around the end of the tubing and pushes the plunger to the surface. This intermittent operation is normally repeated several times per day. Plunger-lift is especially appropriate in these four applications:
Gas Wellsxe2x80x94eliminates liquid loading. As production velocity drops, wells tend to be less efficient in carrying their own liquids to the surface. The introduction of a plunger in this type well reestablishes the original production decline curve, increasing the economic life of the well. At the same time, it generally reduced the volume of injection gas required.
High Ratio Oil Wellsxe2x80x94Can increase the economic life of this type well. By producing the well in an intermittent fashion, the well""s own energy can be used. The need for other, more costly, lifting options can be eliminated.
Intermittent Gas Lift Wellsxe2x80x94Most intermittent gas-lift wells suffer from liquid fallback. This fallback tends to increase the average flowing bottom hole pressure, thus reducing production. With the plunger serving as a mechanical interface, liquids cannot fall back, but are all brought to the surface.
Paraffin and Hydrate Controlxe2x80x94Most plungers have sealing elements that make contact with the inside walls of the tubing. As the plunger travels from the bottom of a well to the surface, the tubing is kept wiped clean, therefore eliminating the buildup or accumulation of paraffin, hydrates, scale and so forth.
Although automatic controllers are available for controlling the operation of plunger lift systems, namely opening and closing the flow line valve, the operation cannot be optimized unless the position of the plunger is known, particularly with respect to the engagement of the plunger with the fluid in the well and critical well performance parameters are determined.
One embodiment of the present invention is a method for determining the depth of a plunger positioned in a tubing string which is located in a wellbore. The interior of the tubing string is acoustically monitored to detect sounds produced by the plunger as it passes tubing collar recesses. The number of the sounds are counted as the plunger passes the recesses. A determination of depth of the plunger in the tubing string is calculated as a function of the number of the sounds which have been counted and the length of tubing joints in the tubing string.
A further embodiment is a method for determining the position of a plunger which is positioned in a tubing string that is located in a well bore, with respect to the fluid in the wellbore. The interior of the tubing string is acoustically monitored to produce a monitored signal as the plunger descends through the tubing string. An acoustic amplitude of the signal is determined over a moving period of time and the present valve of the acoustic amplitude is compared with one or more previous values of the acoustic amplitude to determine when the present value is less than the previous values by a predetermined amount. An indicator is generated to show that the plunger has reached the fluid when it has been determined that the present value of the acoustic amplitude is less than one or more of the previous values of the acoustic amplitude by the predetermined amount.
A further embodiment is a method for determining the position of a plunger, which is positioned in a tubing string that is located in wellbore, with respect to fluid in the wellbore. Gas pressure in the tubing string is monitored at the surface of the wellbore as the plunger descends through the tubing string toward the fluid in the wellbore. Changes in the pressure are detected. A determination is made when the pressure has increased by a predetermined amount within a predetermined time. An indicator is generated to show that the plunger has reached the fluid when it has been determined that the pressure has increased by said predetermined amount within said predetermined time.
A further embodiment is a method for determining the depth from the surface of a wellbore of a plunger positioned in a tubing string which is located in the wellbore. The interior of a tubing string is acoustically monitored at the wellbore surface to detect the sound produced by the plunger as it passes a tubing collar recess, wherein the sound travels from the plunger to the wellbore surface and is received in a first occurrence and the sound reflects from the upper end of the tubing and travels back to the plunger, and the sound reflects from the plunger and travels to the wellhead surface and is received in a second occurrence. The distance from the wellbore surface to the plunger is determined as a function of the time difference and acoustic velocity of the sound in the gas.
A further embodiment is a method for determining the depth of a plunger in a tubing string which is located in a wellbore. Gas pressure in the tubing string is monitored to produce a pressure signal as the plunger descends downward from the upper end of the tubing string. The plunger causes variations in gas pressure within the tubing string as the plunger passes tubing collar recesses in the tubing string. Variations in tubing gas pressure are counted as they are produced by the plunger in the pressure signal. The depth of the plunger is determined in the tubing string is a function of the counted number of variations in tubing gas pressure and the length of the tubing joints in the tubing string.
A further method of the present invention is determining the depth of a plunger in a tubing string which is located in a wellbore. The gas pressure in the tubing string is sampled to produce a pressure signal as the plunger descends downward from the upper end of the tubing string. The plunger causes variations in gas pressure within the tubing string as the plunger passes tubing collar recesses in the tubing string. The gas pressure is sampled at a rate such that a plurality of samples are collected during the time in which the acoustic pulse from a plunger passing a collar recess. The variations in tubing gas pressure are counted in the pressure signal and these variations are produced by the plunger. The depth of the plunger in the tubing string is determined as a function of the counted number of variations in the tubing gas pressure and the length of tubing joints in the tubing string.
A further method of the present invention is determining the depth of a plunger in a tubing string which is located in a wellbore. Gas pressure is sampled in the tubing string to produce a pressure signal as the plunger descends downward from the upper end of the tubing string. The plunger causes variations in gas pressure within the tubing string as the plunger passes tubing collar recesses in the tubing string. The gas pressure is sampled at a rate sufficiently fast to capture in the pressure signal the variations in gas pressure produced as the plunger passes tubing collar recesses in the tubing string. The variations in tubing gas pressure are counted in the pressure signal and the depth of the plunger in the tubing string is determined as a function of the counted number of variations in tubing gas pressure and the length of tubing joints in the tubing string.
A further method of the present invention is determining when a plunger in a tubing string, which is located in a borehole, reaches fluid at the lower end of the tubing string. The interior of the tubing string is acoustically monitored to detect a sound produced by said plunger as it passes each of a plurality of tubing collar recesses in the tubing string. A determination is made when a predetermined period of time has passed without receiving one of the sounds produced by the plunger as it passes said collar recesses. An indicator is generated to show that the plunger has reached the fluid when the predetermined period of time has passed without receiving one of the sounds produced by said plunger as it passes said collar recesses.
A further method of the present invention is determining when a plunger in the tubing string, which is located in a borehole, reaches fluid at the lower end of the tubing string. Gas pressure in the interior of the tubing string is monitored to produce a pressure signal as the plunger descends downward from the upper end of the tubing string. The plunger causes variations in gas pressure within the tubing string as the plunger passes tubing collar recesses in the tubing string. A determination is made when a predetermined period of time has passed without receiving one of the pressure variations produced by the plunger as it passes the collar recesses. An indicator is generated to show that the plunger has reached the fluid when the predetermined period of time has passed without receiving one of the pressure variations produced by the plunger as it passes the collar recesses.
A further embodiment of the present invention is a method for producing a display for indicating performance of a plunger lift system for a wellbore which has a tubing string installed therein. A plunger is located in the tubing string. A schematic of a wellbore is produced on a display screen and the display includes a representation of the plunger in the tubing string. Gas pressure in the tubing string is monitored to produce a pressure signal which includes gas pressure variations caused by the plunger passing tubing collar recesses in the tubing string. The tubing gas pressure variations are counted in the pressure signal to produce a count number. The depth of the plunger in the tubing string is determined as a function of the count number in the tubing joint length for the tubing joints comprising the tubing string. The plunger representation in the wellbore schematic is positioned at the plurality of positions which are a function of the depths determined for the plunger in the tubing string.
A further embodiment of the present invention is a method for producing a display for indicating performance of a plunger lift system for a wellbore which has a tubing string installed therein. A plunger is located in the tubing string. A schematic of a wellbore is produced on the display screen and the display includes a representation of the plunger in the tubing string. The interior of the tubing string is acoustically monitored to detect sounds produced by the plunger as the plunger passes tubing collar recesses of the tubing string. Each sound is associated with one of the tubing collar recesses. A plurality of the sounds produced by the plunger are counted to produce a count number. A depth of the plunger is determined in the tubing string as a function of the count number and tubing joint length for tubing joints comprising the tubing string. The plunger representation is positioned is the wellbore schematic at a plurality of positions which are a function of the depths determined for the plunger in the tubing string.
A further embodiment of the present invention is a method for evaluating the production performance of a wellbore which has a plunger lift system in which a plunger is located within a tubing string which is positioned in the wellbore. The casing pressure of the borehole is monitored. The tubing pressure is monitored within the tubing string to produce a tubing pressure signal. One of more parameters relating to the production performance of the borehole is calculated wherein the parameters are based on the monitored casing pressure and the monitored tubing pressure. The depth of the plunger in the tubing string is determined based upon data in the tubing pressure signal.
A further aspect of the invention is developing an animation of a well schematic with the plunger and liquid slug moving in the tubing string as measured for position.
A further aspect is displaying of well production parameters to an operator along or in conjunction with well schematics.